The present invention relates to an accelerated method for producing a tank, in particular a motor vehicle tank, for storing fuel in a low-temperature state.
Fuels in a low-temperature state are increasingly used nowadays as an energy source for driving vehicles or motor vehicles. EP 1 546 601 A1 describes a pressure container for the mobile and reversible storage of cryogenic vehicle fuels. The pressure container includes an inner container for receiving a cryogenic vehicle fuel and an outer container which surrounds the inner container. Between the inner container and the outer container there is a vacuum which serves for thermally insulating the cryogenic vehicle fuel stored in the inner container. The vacuum here is generated in an evacuation process lasting over a number of days, wherein the outer tank has to be kept at temperatures of approximately 100-120° C. by an external heat source. This requires a high technical, energy and time outlay and therefore causes high costs for the manufacturing of the pressure container.
Starting from this prior art, it is the object of the present invention to provide a method for producing a tank for storing fuel in a low-temperature state, which method can be carried out in an energy-efficient manner and can be used cost-effectively without a high time and technical outlay.
This and other objects are achieved by a method for producing a tank for storing a fuel in a low-temperature state, comprising an inner tank receiving the fuel, an outer skin surrounding the inner tank and an insulating layer arranged between the inner tank and the outer skin. The method according to the invention includes the following steps: i) introducing fuel into the inner tank, a temperature of 30° C. to 120° C., preferably of 70° to 85° C., being obtained by the fuel in the inner tank, and ii) generating a negative pressure in an insulating layer arranged between the inner tank and the outer skin. Examples which can be mentioned as possible fuels include liquid hydrogen, cryogenic hydrogen in the supercritical state, liquid natural gas and other liquefied or low-temperature gases which are stored, in particular, as an energy source for driving a vehicle or a motor vehicle.
The method according to the invention makes it possible to dispense with the technically complicated use of external heating apparatuses for heating the outer skin in order to generate negative pressure and in order to produce a vacuum. The heating temperature for the evacuation operation in the insulating layer is applied by the fuel introduced into the inner tank. The wall of the inner tank is also heated by the temperature obtained in the inner tank. Heat is then transmitted to the adjacent insulating layer via the wall. This operation of transmitting heat from the inside outward is substantially more energy efficient than a transmission of heat by means of a heated outer container since, firstly, the inner tank is not exposed to any external environmental factors influencing the temperature. Secondly, the increasing reduction in pressure in the insulating layer brings about an increasingly better thermal insulation of the inner tank, as a result of which the temperature in the inner tank can be maintained for a longer period, without the use of further energy, or only drops very slowly, which accelerates the evacuation process and promotes the energy efficiency thereof.
According to an advantageous development, a temperature of 30° C. to 120° C., preferably of 70° C. to 85° C., is obtained in the inner tank by the fuel being preheated before being introduced into the inner tank. In other words, this involves hot filling which improves the production process. The hot fuel can be consumed following the evacuation process and new low-temperature fuel can be filled into the inner tank.
As an alternative thereto, optionally also in combination therewith, the temperature of 30° to 120° C., preferably of 70° C. to 85° C. is obtained by the fuel being heated in the inner tank. This can take place, for example, by way of a heat exchanger provided in the inner tank.
In order to provide very good thermal insulation of a fuel when the tank produced according to the invention is used, the negative pressure is preferably generated in such a manner that an absolute pressure in the insulation layer is 10−3 mbar to 10−5 mbar.
Further advantageously, a temperature of the fuel upon introduction into the inner tank is 0° C. to 70° C., preferably 20° C. to 50° C. Fuels which are customarily used can be handled very readily within the stated temperature ranges. Owing to the compressibility of said fuels, when the fuel is filled into the inner tank, a sufficient heating temperature of at least 30° C., and preferably of at least 70° C. to at maximum 85° C., can consequently be very easily obtained.
In order to accelerate the evacuation process, the negative pressure is preferably generated by way of a vacuum pump, in particular by a turbomolecular pump.
The method is furthermore advantageously developed in such a manner that: i) the generating of negative pressure, or ii) the introducing of the heated fuel and the generating of negative pressure, are carried out in a mobile manner, preferably in a vehicle tank or motor vehicle tank arranged on a vehicle, in particular a motor vehicle. This permits location-independent production of the tank, as a result of which the manufacturing time of a vehicle or motor vehicle with the tank produced according to the invention can be kept short at the factory.
By the method according to the invention being carried out within the context of a first filling of the tank, further manufacturing time can be saved. In addition, the fuel introduced into the inner tank for the evacuation process can be immediately used for generating energy.
The method according to the invention is furthermore advantageously suitable for producing a cryo pressure tank which is designed for receiving hydrogen in a supercritical state as the fuel.
On the basis of the solutions according to the invention and the developments thereof, the following advantages are afforded:
1) the method is highly energy efficient and can therefore be used cost-effectively;
2) the method can be carried out independently of location,
3) manufacturing times required at the factory are reduced by the method, and
4) the method can be used without a high technical outlay.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.